The proposed work will be a continuation of work in progress on the origin and nature of ribosomal genes not integrated into the DNA of the chromosome in Drosophila melanogaster. We have shown that in certain genotypes about 40% of the ribosomal genes are not integrated into the DNA of the chromosome in both diploid and polytene tissue. Unintegrated genes have been found in the polytene larval salivary gland in every genotype so far examined. Future work will attempt to relate this phenomenon to the known phenomena of ribosomal gene magnification and compensation. BIBLIOGRAPHIC REFERENCES: C. Zuchowski, A.G. Harford (1976). Biophys. J. 16, 226a (1976), On the Chromosomal Integration of Disproportionately Replicated Ribosomal Genes. C. Zuchowski, A.G. Harford (1976). J. Cell Biol. Extrachromosomal Ribosomal Genes in Diploid and Polytene Tissue of Drosophila Melanogaster.